Precalculus (Stitz-Zeager), Section 11.2: The Law of Sines
by Carl Stitz and Jeff Zeager · Mathematics LibreTexts
Open-textbook section proving the Law of Sines separately for acute, obtuse, and right triangles, then systematizing the ambiguous SSA case into zero, one, or two triangles. Includes bearing and navigation applications and 38 answered exercises.
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Eleven-minute blackboard derivation of both laws in one sitting, dropping altitudes in an oblique triangle and handling the obtuse configuration rather than asserting the formulas. Builds the geometric reason the ratios hold before any problem-solving.
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